Cardiac stimulation system

ABSTRACT

Some embodiments of pacing systems employ wireless electrode assemblies to provide pacing therapy. The wireless electrode assemblies may wirelessly receive energy via an inductive coupling so as to provide electrical stimulation to the surrounding heart tissue. In certain embodiments, the wireless electrode assembly may include one or more biased tines that shift from a first position to a second position to secure the wireless electrode assembly into the inner wall of the heart chamber.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.16/008,562, filed Jun. 14, 2018, which is a continuation of U.S.application Ser. No. 14/044,094, filed Oct. 2, 2013, now U.S. Pat. No.10,022,538 which is a continuation of U.S. application Ser. No.11/549,352, filed Oct. 13, 2006, now abandoned, which claims priority toU.S. Provisional Application Ser. No. 60/748,964 filed on Dec. 9, 2005,the contents of each of which are incorporated herein by reference.

TECHNICAL FIELD

This document relates to systems that electrically stimulate cardiac orother tissue.

BACKGROUND

Pacing instruments can be used to treat patients suffering from a heartcondition, such as a reduced ability to deliver sufficient amounts ofblood from the heart. For example, some heart conditions may cause or becaused by conduction defects in the heart. These conduction defects maylead to irregular or ineffective heart contractions. Some pacinginstruments (e.g., a pacemaker) may be implanted in a patient's body sothat pacing electrodes in contact with the heart tissue provideelectrical stimulation to regulate electrical conduction in the hearttissue. Such regulated electrical stimulation may cause the heart tocontract and hence pump blood.

Conventionally, pacemakers include a pulse generator that is implanted,typically in a patient's pectoral region just under the skin. One ormore wired leads extend from the pulse generator so as to contactvarious portions of the heart. An electrode at a distal end of a leadmay provide the electrical contact to the heart tissue for delivery ofthe electrical pulses generated by the pulse generator and delivered tothe electrode through the lead.

The use of wired leads may limit the number of sites of heart tissue atwhich electrical energy may be delivered. For example, most commerciallyavailable pacing leads are not indicated for use in the left side of theheart. One reason is that the high pumping pressure on the left side ofthe heart may cause a thrombus or clot that forms on a bulky wired leadto eject into distal arteries, thereby causing stroke or other embolicinjury. Thus, in order to pace the left side of the heart with a wiredlead, most wired leads are directed through the cardiac venous system toa site (external to the left heart chambers) in a cardiac vein over theleft side of the heart. While a single lead may occlude a cardiac veinover the left heart locally, this is overcome by the fact that othercardiac veins may compensate for the occlusion and deliver more blood tothe heart. Nevertheless, multiple wired leads positioned in cardiacveins can cause significant occlusion, thereby limiting the number ofheart tissue sites at which electrical energy may be delivered to theleft side of the heart.

Some pacing systems may use wireless electrodes that are attached to theepicardial surface of the heart (external to the heart chambers) tostimulate heart tissue. In these systems, the wireless electrodes arescrewed into the outside surface of the heart wall, which can reduce theeffectiveness of the electrical stimulation in some circumstances.

SUMMARY

Some embodiments of pacing systems employ wireless electrode assembliesto provide pacing therapy. The wireless electrode assemblies may receiveenergy via an inductive coupling so as to provide electrical stimulationto the surrounding heart tissue. In certain embodiments, a wirelesselectrode assembly may be directed through a guide catheter in a heartchamber to deliver at least a portion of the wireless electrode assemblythrough the endocardium. For example, the electrode assembly may includefirst and second fixation devices to secure the electrode assembly tothe heart chamber wall. In such circumstances, the first fixation devicemay oppose rearward migration of the electrode assembly out of the heartchamber wall, and the second fixation device may oppose forwardmigration into the heart chamber wall. Accordingly, the wirelesselectrode assembly can be readily secured to the heart chamber wall andincorporated into the surrounding heart tissue over a period of time.

In some embodiments, a wireless electrode assembly may include a bodyportion that at least partially contains a circuit to electricallystimulate an electrode. The wireless electrode assembly may also includefirst and second biased tines to shift from a loaded condition to anoutwardly extended condition to secure the body portion to a heartchamber wall. The first and second biased tines may be generally opposedto one another.

Particular embodiments may include an electrode delivery system fordelivering a wireless electrode assembly into a heart chamber. Thesystem may include a wireless electrode assembly including a bodyportion and first and second biased tines to shift from a loadedcondition to an outwardly extended condition to secure the body portionto a heart chamber wall. The first and second biased tines may opposeone another. The system may also include a delivery catheter to directthe wireless electrode assembly through a heart chamber and toward aheart chamber wall. The delivery catheter may include an opening in adistal end such that, when the wireless electrode assembly is separatedfrom the opening in the distal end of the catheter, the first and secondbiased tines shift from the loaded condition to the outwardly extendedcondition.

Some embodiments may include a method of inserting a wireless electrodeassembly into a heart chamber wall. The method may include inserting afirst biased tine of a wireless electrode assembly through a portion ofendocardium and into a heart chamber wall. The first biased tine mayshift from a loaded condition to an outwardly extended condition tosecure the body portion to a heart chamber wall. The method may alsoinclude causing a second biased tine of the wireless electrode assemblyto shift from the loaded condition to the outwardly extended conditionto secure the body portion to a heart chamber wall. The first and secondbiased tines may be generally opposed to one another when in theirrespective outwardly extended conditions.

These and other embodiments described herein may provide one or more ofthe following advantages. First, the wireless electrode assemblies mayeliminate or otherwise limit the need for wired pacing leads, therebyreducing the risk of stroke or other embolic injury from a thrombus orclot and reducing the risk of occluding cardiac veins (external to theheart chambers). Second, the wireless electrode assemblies may besecured to the inner wall of one more heart chambers, which may providemore efficient transfer of electrical stimulation. Third, the wirelesselectrode assemblies may be secured to a heart chamber wall in a mannerthat opposes both forward migration and rearward migration of theelectrode assembly. In such circumstances, the secure attachment of thewireless electrode assembly with the heart wall may increase thelikelihood of incorporating the electrode assembly into surroundingtissue, thereby further reducing the likelihood of forming a thrombus orclot in the heart chamber.

The details of one or more embodiments of the invention are set forth inthe accompanying drawings and the description below. Other features,objects, and advantages of the invention will be apparent from thedescription and drawings, and from the claims.

DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view of a stimulation system and at least aportion of an electrode delivery system, in accordance with someembodiments of the invention.

FIG. 2 is a diagram of at least a portion of a device of the stimulationsystem of FIG. 1 .

FIG. 3 is a diagram of at least a portion of a wireless electrodeassembly of the stimulation system of FIG. 1 .

FIG. 4 is a section view of a heart and at least a portion of theelectrode delivery system of FIG. 1 .

FIG. 5 is a perspective view of a wireless electrode assembly, inaccordance with some embodiments of the invention.

FIG. 6 is a perspective view of a wireless electrode assembly, inaccordance with some embodiments of the invention.

FIGS. 7A-D are partial cross-sectional views of the delivery of thewireless electrode assembly of FIG. 5 .

FIG. 8 is a partial cross-sectional view of the delivery of the wirelesselectrode assembly of FIG. 6 .

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

Referring to FIG. 1 , an electrical stimulation system 10 may includeone or more wireless electrode assemblies 120. The wireless electrodeassemblies 120 are implanted within chambers of the heart 30. In thisexample, there are two implanted in the left ventricle 34 and twoimplanted in the right ventricle 38, but the wireless electrodeassemblies may be implanted in the left atrium 32, the right atrium 36,or both. As described below in connection with FIGS. 4-8 , the wirelesselectrode assemblies 120 may be delivered to one or more chambers of theheart 30 using an electrode delivery system 100. The electrode deliverysystem may include a guide catheter 110 that is directed through one ormore veins or arteries to the targeted chamber of the heart 30 (e.g.,the left ventricle 34 is the targeted chamber in the embodiment shown inFIG. 1 ). After the guide catheter 110 is deployed into the targetedheart chamber the wireless electrode assemblies 120 may be consecutivelydelivered through the guide catheter 110 using at least one deliverycatheter 115, which may include a steering mechanism (e.g., steeringwires, a shape memory device, or the like) to delivery the wirelesselectrode assembly 120 to the targeted site on the heart chamber wall.

The distal end of each wireless electrode assembly 120 may include oneor more fixation devices, such as tines. As described in more detailbelow in connection with FIGS. 5 and 6 , the tines 132 and 134 cansecure the wireless electrode assembly 120 to the heart chamber wall. Insome embodiments, each of the wireless electrode assemblies 120 mayinclude a circuit comprising an internal coil and an electrical chargestorage device (not shown in FIG. 1 ). As described in more detail belowin connection with FIG. 3 , the internal coil can be inductively coupledwith an external power source coil so as to charge the electrical chargestorage device (e.g., a battery, capacitor or the like) contained withinthe wireless electrode assembly 120. Also, in some embodiments, each ofthe wireless electrode assemblies 120 has a triggering mechanism in thecircuit to deliver stored electrical charge to adjacent heart tissue(some examples are described in more detail below in connection withFIG. 3 ). In alternative embodiments, one or more of the wirelesselectrode assemblies 120 may have no energy storage device. In suchcircumstances, each wireless electrode assembly may be comprised, forexample, of a ferrite core having caps at each end with ring electrodesencircling the caps. A number of turns of fine insulated wire may bewrapped around the central portion of the core so as to receive energyfrom a magnetic field produced by a shaped driving signal and designedto activate the electrodes.

Referring still to FIG. 1 , the system 10 may also include a pacingcontroller 40 and a transmitter 50 that drives an antenna 60 forcommunication with the wireless electrode assemblies 120. The pacingcontroller 40 includes circuitry to sense and analyze the heart'selectrical activity, and to determine if and when a pacing electricalpulse needs to be delivered and by which of the wireless electrodeassemblies 120. The sensing capability may be made possible by havingsense electrodes included within the physical assembly of the pacingcontroller 40. Alternatively, a conventional single or dual leadpacemaker may sense the local cardiac electrocardiogram (ECG) andtransmit this information to antenna 60 for use by controller 40 indetermination of the timing of wireless electrode assembly firing. Ineither case, the wireless electrode assembly 120 need not be providedwith sensing capability, and also the wireless electrode assemblies 120need not be equipped with the capability of communicating to the pacingcontroller 40 (for example, to communicate information about sensedelectrical events). In alternative embodiments, the wireless electrodeassemblies may communicate sensed information to each other and/or tothe controller 40.

The transmitter 50—which is in communication with, and is controlled by,the pacing controller 40—may drive an RF signal onto the antenna 60. Inone embodiment, the transmitter 50 provides both (1) a charging signalto charge the electrical charge storage devices contained within thewireless electrode assemblies 120 by inductive coupling, and (2) aninformation signal, such as a pacing trigger signal, that iscommunicated to a selected one or more of the wireless electrodeassemblies 120, commanding that wireless electrode assembly 120 deliverits stored charge to the adjacent heart tissue.

One parameter of the wireless electrode assembly 120 that may affect thesystem design is the maximum energy required to pace the ventricle 34,38 or other chamber of the heart 30. This energy requirement can includea typical value needed to pace ventricular myocardium, but also caninclude a margin to account for degradation of contact between theelectrodes and tissue over time. In certain embodiments, each wirelesselectrode assembly 120 may require the maximum pacing threshold energy.This threshold energy is supplied to the wireless electrode assembliesbetween heartbeats by an external radio frequency generator (which mayalso be implanted), or other suitable energy source that may beimplanted within the body. Parameter values for some embodiments may be:

-   -   Threshold pacing voltage=2.5 Volts    -   Typical lead impedance=600 Ohms    -   Typical pulse duration=0.4 mSec    -   Derived threshold energy=4 micro-Joules

Because RF fields at frequencies higher than about 200 kHz may beattenuated by the body's electrical conductivity and because electricfields of any frequency may be attenuated within the body, energytransmission through the body may be accomplished in some embodimentsvia a magnetic field at about 20-200 kHz (or by a magnetic field pulsethat contains major frequency components in this range) and preferablyby transmission of magnetic fields in the range of 100-200 kHz whentransmission is through relatively conductive blood and heart muscle.

Still referring to FIG. 1 , the pacing controller 40 and the transmitter50 may be housed in a single enclosure that is implantable within apatient. In such a configuration, the single enclosure device may have asingle energy source (battery) that may be either rechargeable ornon-rechargeable. In another configuration, the pacing controller 40 andthe transmitter 50 may be physically separate components. As an exampleof such a configuration, the pacing controller 50 may be implantable,for example in the conventional pacemaker configuration, whereas thetransmitter 50 (along with the antenna 60) may be adapted to be wornexternally, such as in a harness that is worn by the patient. In thelatter example, the pacing controller 40 would have its own energysource (battery), and that energy would not be rechargeable given therelatively small energy requirements of the pacing controller 40 ascompared to the energy requirements of the transmitter 50 to be able toelectrically charge the wireless electrode assemblies 120. In this case,the pacing controller 40 would sense the local cardiac ECG signalthrough a conventional pacing lead, and transmit the sensed informationto the external controller. Again, transmission of information, asopposed to pacing energy, has a relatively low power requirement, so aconventional pacemaker enclosure and battery would suffice.

The external programmer 70 is used to communicate with the pacingcontroller 40, including after the pacing controller 40 has beenimplanted. The external programmer 70 may be used to program suchparameters as the timing of stimulation pulses in relation to certainsensed electrical activity of the heart, the energy level of stimulationpulses, the duration of stimulation pulse (that is, pulse width) etc.The programmer 70 includes an antenna 75 to communicate with the pacingcontroller 40, using, for example, RF signals. The implantable pacingcontroller 40 is accordingly equipped to communicate with the externalprogrammer 70, using, for example, RF signals. The antenna 60 may beused to provide such communications, or alternatively, the pacingcontroller 40 may have an additional antenna (not shown in FIG. 1 ) forexternal communications with the programmer 70, and in an embodimentwhere the transmitter 50 and antenna 60 are housed separately from thecontroller 40, for communications with the transmitter 50.

Still referring to FIG. 1 , at least a portion of the system 10 is shownas having been implanted in a patient, and in addition, the programmer70 is also shown that is external to the patient. The controller 40 andtransmitter 50 may be housed in a device that is shaped generallyelongate and slightly curved so that it may be anchored between two ribsof the patient, or possibly around two or more ribs. In one example, thehousing for the controller 40 and transmitter 50 is about 2 to 20 cmlong and about 1 to 10 centimeters cm in diameter, may be about 5 to 10cm long and about 3 to 6 cm in diameter. Such a shape of the housing forthe controller 40 and transmitter 50, which allows the device to beanchored on the ribs, may provide an enclosure that is larger andheavier than conventional pacemakers, and may provide a larger batteryhaving more stored energy. In addition, the controller 40 may comprise adefibrillator that discharges energy to the heart 30 through electrodeson the body of controller 40 when fibrillation is sensed. Other sizesand configurations may also be employed as is practical.

In some embodiments, the antenna 60 may be a loop antenna comprised of along wire that is electrically connected across an electronic circuitcontained within the controller/transmitter housing, which circuitdelivers pulses of RF current to the antenna 60, generating a magneticfield in the space around the antenna 60 to charge the wirelesselectrode assemblies 120, as well as RF control magnetic field signalsto command the wireless electrode assemblies 120 to discharge. In suchembodiments, the antenna 60 may comprise a flexible conductive materialso that it may be manipulated by a physician during implantation into aconfiguration that achieves improved inductive coupling between theantenna 60 and the coils within the implanted wireless electrodeassemblies 120. In one example, the loop antenna 60 may be about 2 to 22cm long, and about 1 to 11 cm wide, and may be about 5 to 11 cm long,and about 3 to 7 cm wide. Placement of the antenna 60 over the ribs mayprovide a relatively large antenna to be constructed that has improvedefficiency in coupling RF energy to the pacing wireless electrodeassemblies 120.

As shown in FIG. 1 , some embodiments of the system 10 may also includea pulse generator device 90 (or pacemaker device) and associated wiredleads 95 which extend from the pulse generator device 90 and into one ormore chambers of the heart 30 (e.g., into the right atrium 36). Forexample, the system 10 may include wired leads 95 from the pulsegenerator device 90 that extend into the right atrium 36 and the rightventricle 38 while wireless electrode assemblies are disposed in theleft atrium 32 and the left ventricle 34. The pulse generator device 90may be used to sense the internal ECG, and may also communicate with thecontroller 40 and/or transmitter 50 as previously described.

As previously described, in some embodiments, each of the wirelesselectrode assemblies 120 includes a rechargeable battery or other chargestorage device. This battery may provide power for delivering pacingenergy to the tissue, and for operating communications, logic, andmemory circuitry contained within the assembly. In some alternativeembodiments, a transmitter and an antenna may be external to the patient(as opposed to the implantable transmitter 50 and antenna 60 depicted inFIG. 1 ), and may serve to recharge the batteries within the electrodeassemblies. The recharge transmitter and antenna may be incorporatedinto furniture, incorporated into the patient's bed, or worn by thepatient (e.g., in a vest-type garment). Daily recharging forpredetermined to periods (e.g., about 30 minutes) may be required insome cases. In these circumstances, the wireless electrode assemblies120 may be autonomous pacemaker-like devices, which can sense the localelectrogram and only pace when the local tissue is not refractory. Suchelectrodes may communicate with the programming unit 70 to receivepacing instructions and transmit data stored in local memory. In theseembodiments, each wireless electrode assembly 120 may also communicatewith other implanted wireless electrode assemblies 120. For example, oneelectrode assembly 120 in the right atrium may be designated as the“master,” and all other implanted electrodes are “'slaves,” that pacewith pre-programmed delays relative to the “'master.” As such, a masterelectrode in the right atrium may only sense the heart's sinus rhythm,and trigger pacing of the slaves with programmed delays.

Referring to FIG. 2 , an embodiment of a device 80 including thecontroller 40, transmitter 50, associated antenna 60 is shown in blockdiagram form. Included within the device 80 is: a battery 82, which maybe recharged by receiving RF energy from a source outside the body viaantenna 60; ECG sensing electrodes 84 and associated sensing circuitry86; circuitry 87 for transmitting firing commands to the implantedwireless electrode assemblies, transmitting status information to theexternal programmer, receiving control instructions from the externalprogrammer and receiving power to recharge the battery; and a controlleror computer 88 that is programmed to control the overall functioning ofthe pacing control implant. In alternative embodiments, antenna 60 mayreceive signals from the individual wireless electrode assemblies 120containing information regarding the local ECG at the site of eachwireless electrode assembly, and/or the antenna 60 may receive signalsfrom a more conventional implanted pacemaker regarding the ECG signal atthe sites of one or more conventional leads implanted on the right sideof the heart.

Referring to FIG. 3 , some embodiments of a wireless electrode assembly120 may include a receiver coil 122 that is capable of being inductivelycoupled to a magnetic field source generating a time-varying magneticfield at the location of coil 122, such as would be generated by thetransmitter 50 and the antenna 60 depicted in FIG. 1 . The RF current inthe external antenna may be a pulsed alternating current (AC) or apulsed DC current, and thus the current induced through the receivercoil 122 would likewise be an AC or pulsed DC current. The currentinduced in coil 122 may be proportional to the time rate of change ofthe magnetic field generated at the site of coil 122 by the external RFcurrent source. In some embodiments, a four-diode bridge rectifier 123may connected across the receiver coil 122 to rectify the AC or pulsedDC current that is induced in the receiver coil 122. A three-positionswitch device 124 may be connected so that when the switch device 124 isin a first position, the rectifier 123 produces a rectified output thatis imposed across a capacitor 125. As such, when the switch device 124is in the position 1 (as is the case in FIG. 4 ), the capacitor 125stores the induced electrical energy.

The switch device 124, in this example, is a voltage-controlled deviceand is connected to sense a voltage across the capacitor 125 todetermine when the capacitor 125 has been sufficiently charged to aspecified pacing threshold voltage level. When the capacitor 125 issensed to have reached the specified pacing threshold level, thevoltage-controlled switch device 124 moves to a position 2, whichdisconnects the capacitor 125 from the coil 122. With the switch device124 in the position 2, the capacitor 125 is electrically isolated andremains charged, and thus is ready to be discharged. The voltagecontrolled switch device 124 may comprise a solid state switch, such asa field effect transistor, with its gate connected to the output of avoltage comparator that compares the voltage on capacitor 125 to areference voltage. The reference voltage may be set at the factory, oradjusted remotely (e.g., after being implanted) via signals sent fromthe physician programmer unit 70 (FIG. 1 ), received by coil 122 andprocessed by circuitry not shown in FIG. 3 . Any electronic circuitrycontained within the wireless electrode assembly 120, including thevoltage controlled switch, can be constructed with components thatconsume very little power, for example CMOS. Power for such circuitry iseither taken from a micro-battery contained within the wirelesselectrode assembly, or supplied by draining a small amount of chargefrom capacitor 125.

Still referring to FIG. 3 , a narrow band pass filter device 126 mayalso be connected across the receiver coil 122, as well as beingconnected to the three-position switch device 124. The band pass filterdevice 126 passes only a single frequency or communication signal thatis induced in the coil 122. The single frequency of the communicationsignal that is passed by the filter device 126 may be unique for theparticular wireless electrode assembly 120 as compared to otherimplanted wireless electrode assemblies. When the receiver coil 122receives a short magnetic field burst at this particular frequency, thefilter device 126 passes the voltage to the switch device 124, which inturn moves to a position 3.

With the switch device 124 in the position 3, the capacitor 125 may beconnected in series through two bipolar electrodes 121 and 129, to thetissue to be stimulated. As such, at least some of the charge that isstored on the capacitor 125 is discharged through the tissue. When thishappens, the tissue becomes electrically depolarized. In one exampleembodiment described in more detail below, the bipolar electrodes 121and 129 across which stimulation pulses are provided are physicallylocated at opposite ends (e.g., a proximal end and a distal end) of thewireless electrode assembly 120. After a predetermined, or programmed,period of time, the switch returns to position 1 so the capacitor 125may be charged back up to the selected threshold level.

It should be noted that, for sake of clarity, the schematic diagram ofFIG. 3 shows only the electrical components for energy storage andswitching for particular embodiments of the wireless electrode assembly120. Not necessarily shown are electronics to condition the pacing pulsedelivered to the tissues, which circuitry should be understood from thedescription herein. Some aspects of the pulse, for example pulse widthand amplitude, may be remotely programmable via encoded signals receivedthrough the filter device 126 of the wireless electrode assembly 120. Inthis regard, filter 126 may be a simple band pass filter with afrequency unique to a particular wireless electrode assembly, and theincoming signal may be modulated with programming information.Alternatively, filter 126 may consist of any type of demodulator ordecoder that receives analog or digital information induced by theexternal source in coil 122. The received information may contain a codeunique to each wireless electrode assembly to command discharge ofcapacitor 125, along with more elaborate instructions controllingdischarge parameters such as threshold voltage for firing, duration andshape of the discharge pulse, etc.

Using wireless electrode assemblies of the type shown in FIG. 3 , all ofthe implanted wireless electrode assemblies 120 may be chargedsimultaneously by a single burst of an RF charging field from atransmitter antenna 60. Because back reaction of the wireless electrodeassemblies 120 on the antenna 60 may be small, transmitter 50 (FIG. 1 )losses may be primarily due to Ohmic heating of the transmit antenna 60during the transmit burst, Ohmic heating of the receive coil 122, andOhmic heating of conductive body tissues by eddy currents induced inthese tissues by the applied RF magnetic field. By way of comparison, ifeight wireless electrode assemblies 120 are implanted and each isaddressed independently for charging, the transmitter 50 may be turnedON eight times as long, which may require almost eight times moretransmit energy, the additional energy being primarily lost in heatingof the transmit antenna 60 and conductive body tissues. With thewireless electrode assembly 120 of FIG. 3 , however, all implantedwireless electrode assemblies can be charged simultaneously with a burstof RF current in antenna 60, and antenna and body tissue heating occursonly during the time required for this single short burst. Each wirelesselectrode assembly is addressed independently through its filter device126 to trigger pacing. The transmitted trigger fields can be of muchsmaller amplitude, and therefore lose much less energy to Ohmic heating,than the transmitted charging pulse.

Pending U.S. patent application Ser. No. 10/971,550 (filed on Oct. 20,2004), Ser. No. 11/075,375 (filed on Mar. 7, 2005), and Ser. No.11/075,376 (filed on Mar. 7, 2005), all owned by the assignee of thisapplication, describe various features of wireless electrode assemblies,systems to deliver the wireless electrode assemblies to the heart, andelectronic components to activate the wireless electrode assemblies todeliver electrical stimulation. It should be understood from thedescription herein that some of the features described in these threepatent applications (Ser. Nos. 10/971,550, 11/075,375, and 11/075,376)may be applicable to particular embodiments described herein.

Referring now to FIG. 4 , some embodiments of an electrode deliverysystem 100 may include a guide catheter 110 and a delivery catheter 115.The catheters 110 and 115 may comprise an elongate body that extendsfrom a proximal end (outside the patient's body, not shown in FIG. 4 )to a distal end (depicted in FIG. 4 as extending into the patient'sheart 30). The delivery catheter 115 fits within a lumen of the guidecatheter 110, and can be advanced through the guide catheter 110 so thata distal end of the delivery catheter 115 extends out of a distalopening of the guide catheter 110. The guide catheter 110 may bedirected through one or more veins or arteries to the targeted chamberof the heart (e.g., the left ventricle 34 is the targeted chamber in theembodiment shown in FIG. 4 ). The guide catheter 110 may comprise asteering mechanism (e.g., steering wires, shape memory device, or thelike) to shift the distal end and may include at least one marker band112 to permit viewability of the distal end of the guide catheter 110using medical imaging techniques. Such a marker band 112 may aid aphysician when steering the guide catheter 110 to the targeted heartchamber.

After the guide catheter 110 is deployed into the targeted heartchamber, the wireless electrode assemblies 120 may be advanced into theheart tissue through the guide catheter 110 using at least one deliverycatheter 115. The wireless electrode assemblies 120 may be consecutivelydelivered through the guide catheter 110 using at least one deliverycatheter 115. In some embodiments, the delivery catheter 115 may includeat least one marker band 116 to permit viewability of the distal end ofthe delivery catheter 115 using medical imaging techniques. The deliverycatheter 115 may include a steering mechanism (e.g., steering wires,shape memory device, or the like) to shift the distal end. For example,the delivery catheter 115 may comprise a shape memory device (e.g., oneor more wires comprising Nitinol or another shape memory material) toprovide a predetermined curvature near the distal end of the deliverycatheter 115. The shape memory device may be activated by a change inelectrical charge or by a change in temperature. In one example, thedelivery catheter 115 may include a shape memory device near the distalend that is capable of providing a 90-degree deflection curve near thedistal end immediately before a longitudinally straight section at thedistal end of the catheter 115.

In some approaches to the targeted tissue, the steering mechanism (e.g.,steering wires, shape memory device, or the like) of the deliverycatheter 115 can be manipulated so that a deflected portion near thedistal end of the delivery catheter abuts against the septum wall of thetargeted heart chamber. For example, the deflected portion of thedelivery catheter may abut against the septum wall 39 between the leftventricle 34 and the right ventricle 38 while a longitudinally straightsection of the catheter 115 extends the distal end against the targetedheart chamber wall to receive the wireless electrode assembly 120 (referto the dotted-line example depicted in FIG. 4 ). Accordingly, thedeflected portion of the delivery catheter 115 can abut against theseptum wall to support the position of the distal end of the deliverycatheter 115 during the deployment of the wireless electrode assembly120 into the targeted heart tissue 35 (refer, for example, To FIGS. 7A-Dand 8). Such an approach may provide leverage and stability during theinsertion process for the electrode assembly 120.

The delivery catheter 115 includes an opening at the distal end in whichan associated wireless electrode assembly 120 is retained in a loadedposition. The wireless electrode assembly 120 may include a body portionthat has a length and a radius configured to be retained with thedelivery catheter 115. As described in more detail below, someembodiments of the body portion of the wireless electrode assembly 120may have a radius, for example, of about 1.25 mm or less and may have alength, for example, of about 10 mm or less. Wireless electrodeassemblies configured for insertion into an atrial wall may be smallerthan those configured for insertion into the ventricle walls.

In the exemplary embodiment shown in FIG. 4 , the wireless electrodeassemblies 120 comprise a pointed-tip cylindrical body having a forwardportion embedded within the heart wall tissue and a rearward portionthat is inside the heart chamber but not fully embedded in the heartwall tissue. The pointed distal tip 130 of the electrode assembly 120facilitates penetration into the heart wall tissue, and the proximal endof the electrode assembly is configured to remain outside of the heartwall. However, in some embodiments, both the distal tip 130 and theproximal end of the electrode assembly 120 can be embedded within theheart wall tissue 30. As described in more detail below, the electrodeassembly 120 may include two fixation devices 132 and 134 that generallyoppose one another, such as a set of distal tines and a set of proximaltines. The distal tines can be coupled to and extend from a periphery ofa forward portion of the body of the electrode assembly 120, and theproximal tines can be coupled to and extend from a periphery of arearward portion of the body. As described in more detail below, the setof distal tines extend somewhat outwardly from the body of the electrodeassembly 120 but also rearwardly so as to prevent the electrode frombecoming dislodged from the heart wall once the electrode assembly 120is implanted. Also, as described in more detail below, the set ofproximal tines extend somewhat outwardly from the body of the electrodeassembly 120 but also forwardly so as to prevent the electrode assembly120 from penetrating entirely through the heart wall.

As the wireless electrode assembly 120 is deployed from deliverycatheter 115, tines 132 and 134 located externally on the wirelesselectrode assembly 120 may adjust to a deployed position (e.g., anoutwardly extended condition). Such an adjustment to the deployedposition may be caused, for example, due to spring bias of the tines 132and 134 (described in more detail below). When the tines 132 and 134 arein the deployed position, the tines 132 and 134 are capable of securingthe wireless electrode assembly 120 to the targeted tissue site (e.g.,described in more detail below, for example, in connection with FIGS.7-8 ). In some embodiments, the opening at the distal end of thedelivery catheter 115 may be part of conduit that extends through theelongated body of the catheter 115. In other embodiments, the opening atthe distal end of the delivery catheter 115 may extend only a partiallength into the delivery catheter 115 (e.g., with a narrower channelextending fully to the proximal end of the delivery catheter 115 toprovide space for the plunger mechanism 140).

Referring to FIGS. 5 and 6 , the tines 132 and 134 of the wirelesselectrode assembly 120 may be configured in a number of orientations.For example, the tines 132 and 134 can be arranged in a configuration(refer to FIG. 5 ) that permits the electrode assembly 120 to penetratea substantial length into the heart wall tissue (described in moredetail below in connection with FIGS. 7A-7D). In another example, thetines 132 and 134 can be arranged in a configuration (refer to FIG. 6 )that permits the electrode assembly 120 to penetrate a lesser amountinto the heart wall tissue (described in more detail below in connectionwith FIG. 8 ). In some embodiments, wireless electrode assembly 120 mayinclude a proximal electrode 121 at or near a proximal end and a distalelectrode 129 at or near a distal end. The proximal electrode 121 anddistal electrode 129 may provide bipolar electrode capabilities for thewireless electrode assembly 120, thereby permitting the assembly 120 tosupply an electrical charge between the proximal and distal electrodes121 and 129 (and across the nearby heart tissue).

As previously described, the fixation device 132 may include a set ofbiased tines arranged near the distal end of the wireless electrodeassembly 120 so as to secure the wireless electrode assembly 120 to theheart chamber wall. The fixation device 134 may include a first set ofbiased tines arranged near the proximal end of the wireless electrodeassembly 120 which can also serve to secure the assembly 120 to theheart chamber wall. In some embodiments, the tines 134 arranged near theproximal end may have a different configuration and orientation from theopposing tines 132 arranged near the distal end. For example, as shownin the embodiments depicted in FIGS. 5-6 , the distal tines 132 maygenerally oppose the proximal tines 134. In these circumstances, atleast some of the tines 132 and 134 are biased to adjust from a loadedcondition to a deployed condition. For example, when in the loadedcondition, the tines 132 and 134 may be arranged generally along thebody 128 of the wireless electrode assembly 120, within a plurality ofrecesses 136 and 137, respectively, extending longitudinally along anouter surface of the body 128, so as to fit within the cavity at thedistal end of the delivery catheter 115 (refer, for example, to FIG.7A). When the biased tines 134 and 134 are flexed into the loadedcondition, the recesses 136 and 137 receive the tines 132 and 134 tofacilitate slidable engagement between the wireless electrode assembly120 and the delivery catheter 115. The tines 132 and 134 may be biasedto adjust to the deployed condition while advancing from the deliverycatheter 115. When in the deployed condition, the distal tines 132 maybe disposed in an outwardly extended orientation that opposes theoutwardly extended orientation of the proximal tines 134. In oneexample, the distal tip 130 may penetrate into the heart chamber wallwhen a force is applied to the wireless electrode assembly 120 (e.g.,penetrate the endocardium and possibly into the myocardium). Duringpenetration, the tines 132 and 134 are biased to transition from theloaded condition (described in more detail below in connection withFIGS. 7A-D) to the deployed condition as illustrated by tines 132 a and134 a (in FIG. 5 ) and tines 132 b and 134 b (in FIG. 6 ). Such aconfiguration permits the wireless electrode assembly 120 to be readilysecured to the heart chamber wall after advancing from the deliverycatheter 115.

As previously described, the wireless electrode assembly 120 may bearranged in the delivery catheter 115 (FIG. 4 ) so that the tines 132and 134 are in a loaded condition. Thus, when the electrode assembly 120is advanced out of the distal end of the delivery catheter 115, thetines 132 and 134 transition into their respective deployed conditions.In some embodiments, the tines 132 and 134 may comprise biocompatiblematerial that is capable of flexing from the loaded condition to thedeployed condition. For example, one or more of the tines 132 and 134may comprise a shape memory alloy (e.g., Nitinol or the like), stainlesssteel, titanium, metal alloys (e.g., nickel-cobalt base alloys such asMP35N), composite materials, or the like.

In the embodiment depicted in FIG. 5 , the distal tines 132 a andproximal tines 134 a can be arranged so that a substantial length of theelectrode assemble 120 penetrates into the heart wall tissue. In thesecircumstances, the distal tines 132 a may penetrate in the heart walltissue to hinder rearward migration of the electrode assembly 120 backinto the hear chamber, and the proximal tines 134 a are configured toabut or partially penetrate into the wall surface to hinder forwardmigration of the assembly 120 toward the outside of the heart. Thus,when in the deployed condition, the distal tines 132 a oppose migrationof the wireless electrode assembly 120 in the generally proximaldirection and the proximal tines 134 a oppose migration in the generallydistal direction. Accordingly, the opposing orientation of the tines 132a and 134 a secures the wireless electrode assembly 120 to the hearttissue in a manner so that a portion of the proximal end of the wirelesselectrode assembly 120 is not embedded in the heart tissue. Becausetines 132 a and 134 a can retain the electrode assembly 120 in the hearttissue without substantial migration, the proximal end of the electrodeassembly body 128 can be incorporated into the surrounding heart tissueover a period of days or weeks. In these embodiments, the wirelesselectrode assembly 120 may be immobilized by the surrounding tissue toprevent future dislodgement. In such circumstances, the patient mayreceive anti-coagulants, Aspirin, or other drugs (e.g., PLAVIX, CUMODIN,etc.) for several months after the operation or until incorporation ofthe wireless electrode assembly 120 into the surrounding tissue hasoccurred.

In this embodiment depicted in FIG. 5 , the distal tines 132 a and theproximal tines 134 a are slightly curved and are oriented in an opposingmanner when in the deployed condition. The curvature of the proximaltines 132 is such that the tines 134 a contact the surface of the hearttissue near the proximal tines' extremities. In addition, the proximaltines 134 a can be positioned along the body 128 and curved in a mannerso that the free end 135 a of each proximal tine 134 a abuts orpartially penetrates into the heart wall tissue after a portion of theelectrode assembly 120 has penetrated therein. The wireless electrodeassembly 120 can be advanced into the heart wall tissue 35 so that theproximal tines 134 a cause a slight spring-back action after abutting orpartially penetrating into the heart wall tissue. For example, theproximal tines 134 a may flex outwardly when forced into engagement withthe heart wall tissue, and such an outward flexing action can cause aslight spring back motion to the wireless electrode assembly 120. Thedistal tines 132 a may flex outwardly in response to this slightspring-back motion in the proximal direction, thereby enhancing theengagement of the heart tissue between the distal tines 132 a and theproximal tines 134 a.

Still referring to FIG. 5 , the proximal tines 134 a can be positionedalong the body 128 and curved in a manner so that the free end 135 a ofeach proximal tine 134 a abuts or partially penetrates into the heartwall tissue after a substantial portion of the electrode assembly 120has penetrated therein. For example, in this embodiment, the proximaltines 134 a are configured such that the free end 135 a of each tine 134a (when in the deployed condition) is disposed a longitudinal distanceD₁ rearward of the distal tip 130. In this embodiment, the longitudinaldistance D₁ is greater than half the overall length L of the electrodeassembly 120. In such circumstances, a majority of the length of theelectrode assembly 120 can penetrate into the heart wall tissue beforethe proximal tines 134 a engage the heart wall to oppose forwardmigration. This example of substantial penetration of the electrodeassembly 120 into the heart wall tissue may be effective when advancingthe electrode assembly 120 into portions of the heart having thickermyocardial walls (e.g., some heart walls around the left and rightventricles). In addition, when a substantial portion of the electrodeassembly 120 penetrates into the heart tissue, the non-penetratingproximal portion of the electrode assembly 120 is reduced, therebypromoting efficient healing and incorporation into the surrounding hearttissue.

In the embodiment depicted in FIG. 6 , the distal tines 132 b andproximal tines 134 b can be arranged so that a lesser length of theelectrode assembly 120 penetrates into the heart wall tissue. Forexample, the distal tines 132 b may be substantially different in lengththan the proximal tines 134 b. Also, the proximal tines 134 b may have agreater curvature than the proximal tines 134 a previously described inconnection with FIG. 5 so that the contact between the surface of theheart tissue and the proximal tines is near the apex of the curvature.In these embodiments, the proximal tines 134 b can be positioned alongthe body 128 and curved in a manner so that the curvature apex 135 b ofeach proximal tine 134 b abuts the heart wall tissue after a partiallength of the electrode assembly 120 has penetrated therein. Forexample, the proximal tines 134 b are configured such that the apex 135b (when in the deployed condition) is disposed at a longitudinaldistance D₂ rearward of the distal tip 130. In this embodiment, thelongitudinal distance D₂ is about half the overall length L of theelectrode assembly 120. Accordingly, about half of the electrodeassembly 120 can penetrate into the tissue before the proximal tines 134b oppose forward migration. Such penetration to a limited length of theelectrode assembly 120 may be effective when advancing the electrodeassembly 120 into portions of the heart wall having a reduced wallthickness (e.g., some heart walls around the right atrium).

As previously described, the tines 132 b and 134 b are oriented in anopposing fashion to secure the wireless electrode assembly 120 to theheart tissue in a manner that opposes reward migration and forwardmigration, thereby permitting incorporation into the surrounding tissue.For example, the proximal tines 134 b may flex outwardly when forcedagainst the heart wall tissue, and such an outward flexing action cancause a slight spring back motion to the wireless electrode assembly120. The distal tines 132 b may flex outwardly in response to thisslight spring-back motion in the proximal direction, thereby enhancingthe engagement of the heart tissue between the distal tines 132 b andthe proximal tines 134 b.

In some embodiments, the proximal tines 134 b of the electrode assemblymay be nonaligned with the distal tines 132 b along the body of theelectrode assembly 128. For example, as shown in FIG. 6 , the distaltines 132 b may be tangentially shifted about 45° along the bodycircumference as compared to the proximal tines 134 b so that theproximal tines 134 b and distal tines 132 b are nonaligned. As describedin more detail below in connection with FIG. 8 , such nonalignmentbetween the proximal tines 134 b and the distal tines 132 b can permitone set of tines (e.g., the proximal tines 134 b) to partially deploybefore fully exiting the distal opening of the delivery catheter 115. Inthese circumstances, the partial deployment of the proximal tines 134 bbefore fully exiting the delivery catheter 115 can facilitate theabutting engagement between the proximal tines 134 b and the heartchamber wall.

It should be understood that in some embodiments of the wirelesselectrode assembly 120, the distal tines 132 may also serve as at leasta portion of the distal electrode 129. Also, in some embodiments,proximal tines 134 may also serve as at least a portion of the proximalelectrode 121. For example, the tines 132 and 134 may comprise anelectrically conductive material (e.g., stainless steel or anothermetallic material) and may be electrically connected to the distal andproximal electrode circuitry (respectively).

Referring now to FIGS. 7A-D, some embodiments of the wireless electrodeassemblies 120 may be press fit into the conduit of the deliverycatheter 115 so that a plunger mechanism 144 may be used to separate thewireless electrode assembly 120 from the delivery catheter 115. As shownin FIG. 7A, the delivery catheter 115 may be steered and directed towarda targeted site at the surface of heart tissue 35 (e.g., a heart chamberwall). The delivery catheter 115 may contain at least a distal portionof a tube portion 142 that is coupled to an actuation rod 140. Aspreviously described, in some approaches to the targeted tissue, thesteering mechanism (e.g., steering wires, shape memory device, or thelike) of the delivery catheter 115 can be manipulated so that adeflected portion near the distal end of the delivery catheter 115 abutsagainst the septum wall of the targeted heart chamber. For example, theportion 117 (FIG. 7A) of the delivery catheter 115 may be deflected toabut against the septum wall while a longitudinally straight section ofthe catheter 115 extends toward the targeted heart tissue 35. As such,some portion (e.g., portion 117) the delivery catheter 115 can abutagainst the septum wall to support the position of the distal end of thedelivery catheter 115.

The wireless electrode assembly 120 may be releasably engaged with thetube portion 142. For example, the wireless electrode assembly 120 maybe press-fit into the tube portion 142. In another example, the tubeportion 142 may have a square cross-sectional shape, a hexagonalcross-sectional shape, a keyed cross-sectional shape, or othernoncircular cross-sectional shape to engage the complementary shapedbody of the wireless electrode assembly 120. The tube portion 140 may besubstantially rigid so as to retain the fixation devices 132 and 134 ofthe wireless electrode assembly 120 in a loaded condition (as shown, forexample, in FIG. 7A). In some embodiments, one or both of the actuationrod 140 and the plunger mechanism 144 may extend to an actuation device(e.g., a hand-operated trigger mechanism) at the proximal end of thedelivery catheter 115 outside the patient's body. In some embodiments,the tube portion 142 and the actuation rod 140 may be fixedly arrangedin the delivery catheter 115 so as to deliver one electrode assembly ata time. Alternatively, the tube portion 142 and the actuation rod 140may be movable through lumen of the delivery catheter 115 so that anumber of electrode assemblies can be consecutively passed through thedelivery catheter 115.

As shown in FIG. 7B, the distal end of the delivery catheter 115 mayabout the surface of the heart tissue 35 to prepare the wirelesselectrode assembly 120 for fixation to the tissue 35. In thisembodiment, the distal end of the delivery catheter 115 includes amarker band 116 to facilitate the steering and guidance of the deliverycatheter (e.g., a physician may employ medical imaging techniques toview the marker band 116 while the delivery catheter 115 is in the heart30).

Referring to FIG. 7C, the electrode assembly 120 can be advanced throughthe distal opening of the delivery catheter 115 (and the tube portion142) and into the tissue 35. This operation may be performed byadvancing the plunger mechanism 144 against the proximal end of thewireless electrode assembly 120 to thereby force the distal tip 130 ofthe wireless electrode assembly 120 to penetrate through the endocardiumand possibly into the myocardium. For example, the force may be appliedby manipulating the actuation device (e.g., the hand-operated triggermechanism connected to the proximal end of the plunger mechanism 144) toforce the plunger mechanism 144 in the distal direction relative to theactuation rod 140 (and the tube portion 142). As such, the distal tip130 of the electrode assembly 120 pierces the tissue surface andadvances into the tissue 35.

Referring to FIG. 7D, when the delivery catheter 115 is fully separatedfrom the wireless electrode assembly 120, the fixation devices 132 and134 can transition from a loaded condition to a deployed condition. Inthis embodiment, the fixation devices 132 and 134 comprise tines thatare biased to the deployed condition (refer, for example, to FIGS. 5-6 )after being released from the tube portion 142 of the delivery catheter115. As previously described in connection with FIG. 5 , the tines 132and 134 can be configured so that a substantial portion of the electrodeassembly 120 penetrates into the tissue 35 before the forward migrationis hindered by the proximal tines 134. For example, the electrodeassembly 120 can penetrate the longitudinal length D₁ into the hearttissue 35 so that a majority of the overall length of the electrodeassembly 120 is advanced into the tissue 35. In these embodiments, thedistal tines 132 a can transition to the deployed condition in whicheach tine 132 a is outwardly extended in a generally proximal directionwhen the distal tip 130 penetrates into the heart tissue 35. Also, inthese embodiments, the proximal tines 134 a can transition to thedeployed condition in which each tine 134 a is extended outwardly in agenerally distal direction when the delivery catheter 115 is separatedfrom the proximal end of the wireless electrode assembly 120. Theproximal tines 134 a have a base 150 affixed to the body of electrodeassembly 120.

As previously described, in some circumstances, the proximal tines 134 amay flex outwardly when forced against the heart wall tissue, and suchan outward flexing action can cause a slight spring back motion to thewireless electrode assembly 120. The distal tines 132 a may flexoutwardly in response to this slight spring-back motion in the proximaldirection, thereby enhancing the engagement of the heart tissue 35between the distal tines 132 a and the proximal tines 134 a. Such anopposed orientation of the tines 132 a and 134 a hinders rearwardmigration and forward migration of the electrode assembly 120. Aspreviously described, the tissue 35 may grow and eventually incorporatethe wireless electrode assembly 120 therein, thereby preventing thewireless electrode assembly 120 from dislodgement from the tissue 35. Inthe example depicted in FIG. 7D, the proximal tines 134 a areillustrated as abutting against the heart tissue 35. It should beunderstood that, in some embodiments, the proximal tines 134 a may atleast partially penetrate into the heart tissue 35 when the electrodeassembly 120 is advanced therein.

Referring to FIG. 8 , other embodiments of the wireless electrodeassembly 120 include fixation devices 132 and 134 that transition intodifferent configurations. For example, the fixation devices 132 b and134 b may include tines that are biased to transition into a deployedcondition (after being released from the delivery catheter 115) asdescribed in connection with FIG. 6 . In such embodiments the tines 132b and 134 b may deploy to outwardly extended orientations that generallyoppose one another. The tines 132 and 134 can be configured so that alimited length of the electrode assembly 120 penetrates the tissue 35before the forward migration is opposed by the proximal tines 134 b(e.g., before the curvature apex 135 b abuts the tissue 35). Forexample, the electrode assembly 120 can penetrate the longitudinallength D₂ into the heart tissue 35 so that about half of the overalllength of the electrode assembly 120 is advanced into the tissue 35. Aspreviously described, in some circumstances, the proximal tines 134 bmay flex outwardly when forced against the heart wall tissue 35, andsuch an outward flexing action can cause a slight spring back motion tothe wireless electrode assembly 120. The distal tines 132 b may flexoutwardly in response to this slight spring-back motion in the proximaldirection, thereby enhancing the engagement of the heart tissue 35between the distal tines 132 b and the proximal tines 134 b. Suchopposed orientations of the tines 132 b and 134 b hinders rearward andforward migration of the electrode assembly 120. Also, as previouslydescribed, the tissue 35 may grow and eventually incorporate thewireless electrode assembly 120 therein, thereby preventing the wirelesselectrode assembly 120 from dislodgement from the tissue 35.

Still referring to FIG. 8 , the proximal tines 134 b may be configuredto at least partially deploy before exiting the distal opening of thedelivery catheter 115. As such, the proximal tines 134 b may at leastpartially curve outwardly from the body 128 of the electrode assemblybefore contacting the heart wall tissue 35. In these circumstances, theproximal tines 134 b may curve so as to abut against the heart walltissue 134 b without the extremities of the proximal tines 134 bpenetrating into the tissue 35. Because the proximal tines 134 b can atleast partially deploy before exiting the distal opening of the deliverycatheter 115, the proximal tines 134 b can achieve the greater curvaturepreviously described in connection with FIG. 6 so that the contactbetween the heart tissue 35 and the proximal tines 134 b is near thecurvature apex 135 b (FIG. 6 ).

For example, in some embodiments, electrode assembly 120 can be arrangedin the tube portion 142 so that the proximal tines 134 b are alignedwith deployment slots 146 (FIG. 8 ) formed in the tube portion 142.Accordingly, when the electrode assembly is advanced into the hearttissue 35, the proximal tines 134 b at least partially extend outwardlyinto the deployment slots 146, thereby permitting the proximal tines 134b to partially deploy before exiting the distal opening of the deliverycatheter 115. As previously described in connection with FIG. 6 , theproximal tines 134 b may be nonaligned with the distal tines 132 b alongthe body of the electrode assembly 128. Such nonalignment between theproximal tines 134 b and the distal tines 132 b can permit the proximaltines 134 b to partially deploy in the deployment slots 146 while thedistal tines 132 b are retained against the electrode body 128 in thetube portion 142. Alternatively, the distal tines 132 b can be generallyaligned with the proximal tines 134 b so that both the distal tines 132b and the proximal tines 134 b pass through the deployment slots 146during advancement of the electrode assembly 120 from the deliverycatheter 115. It should be understood that, in some embodiments, thedeployment slots 146 may extend through the distal circumferential endof the delivery catheter 115 so that the proximal tines 134 b can atleast partially deploy through the distal circumferential end of thedelivery catheter 115 before exiting the distal opening of the deliverycatheter 115.

In some embodiments of the delivery catheter 115 described herein, thedelivery catheter 115 may be wholly separate from the actuation rod 140so that the actuation rod 140 slides through a conduit passing throughthe delivery catheter 115. In such circumstances, the actuation rod 140may be completely retracted from the delivery catheter so that a secondwireless electrode assembly may be detachably coupled to the actuationrod 140 (or to an unused, different actuation rod 140) and then directedthrough the delivery catheter 115 already disposed in the patient'sbody. In other embodiments, the delivery catheter 115 and the actuationrod 140 may be coupled to one another. In such circumstances, thedelivery catheter 115 and actuation rod 140 may be removed from theguide catheter 110 (FIG. 4 ) so that a second wireless electrodeassembly may be detachably coupled to the actuation rod 140 (or to apreviously unused delivery catheter/actuation rod having a similarconstruction) and then directed through the guide catheter 110 alreadydisposed in the patient's body.

In some embodiments, the delivery catheter 115 may include a tubeportion that is configured to retain a plurality of wireless electrodeassemblies 120 (e.g., similar to tube portion 142 but having a greaterlength to receive a multitude of assemblies 120). For example, thedelivery catheter may be configured to carry two, three, four, five,ten, twelve, or more electrode assemblies 120 in a serial (end to end)arrangement. As such, the plunger mechanism 144 can be used to forceeach electrode assembly 120 into different tissue sites withoutretracting the delivery catheter out of the heart. As describedpreviously, the actuation mechanism may force the plunger 144 in agenerally distal direction. In the serially arranged embodiment, theplunger 144 applies the force to the most rearward assembly 120 in theserial arrangement, which in turn applies a force from the distal tip130 of the most rearward assembly 120 to the proximal end of the nextassembly 120 in the serial arrangement. In this fashion, the applicationof force can propagate through the serial arrangement until the assembly120 nearest the heart tissue is delivered to the target site (asdescribed previously, for example, in connection with FIG. 7D). Itshould be understood that the serial arrangement may comprise electrodeassemblies 120 as described in connection with FIG. 5 , as described inconnection with FIG. 6 , or some combination thereof.

Some of the embodiments described herein permit a plurality of pacingelectrodes to be deployed at multiple pacing sites. The pacing sites maybe located in the left atrium 32, the left ventricle 34, the rightatrium 36, the right ventricle, or a combination thereof. Furthermore,the pacing electrodes may comprise wired pacing leads 95 (FIG. 1 ),wireless electrode assemblies, or a combination thereof. Providingelectrical stimulation at multiple pacing sites and in multiple heartchambers may be used to treat a number of conditions. One such conditionis congestive heart failure (CHF). It has been found that CHF patientshave benefited from hi-ventricular pacing, that is, pacing of both theleft ventricle 34 and the right ventricle 38 in a timed relationship. Itis believed that many more patients could benefit if multiple sites inthe left and right ventricles 34 and 36 could be synchronously paced. Inaddition, pacing at multiple sites may be beneficial where heart tissuethrough which electrical energy must propagate is scarred ordysfunctional, which condition halts or alters the propagation of anelectrical signal through that heart tissue. In these cases,multiple-site pacing may be useful to restart the propagation of theelectrical signal immediately downstream of the dead or sick tissuearea. Synchronized pacing at multiple sites on the heart may inhibit theonset of fibrillation resulting from slow or aberrant conduction, thusreducing the need for implanted or external cardiac defibrillators.Arrhythmias may result from slow conduction or enlargement of the heartchamber. In these diseases, a depolarization wave that has taken a longand/or slow path around a heart chamber may return to its starting pointafter that tissue has had time to re-polarize. In this way, a neverending “race-track” or “circus” wave may exist in one or more chambersthat is not synchronized with normal sinus rhythm. Atrial fibrillation,a common and life threatening condition, may often be associated withsuch conduction abnormalities. Pacing at a sufficient number of sites inone or more heart chambers, for example in the atria, may force alltissue to depolarize in a synchronous manner to prevent the race-trackand circus rhythms that lead to fibrillation.

A number of embodiments of the invention have been described.Nevertheless, it will be understood that various modifications may bemade without departing from the spirit and scope of the invention.Accordingly, other embodiments are within the scope of the followingclaims.

What is claimed is:
 1. An electrical stimulation system for providepacing therapy to a heart, the system comprising: a pulse generatordevice including a wired lead extending therefrom; and a wirelesselectrode assembly separate from the pulse generator device, thewireless electrode assembly including: a body having a distal end regionextending to a distal end of the body and a proximal end regionextending to a proximal end of the body; a first electrode secured tothe distal end of the distal end region of the body; a second electrodedisposed on the proximal end region of the body; and a tissue fixationmember configured to engage cardiac tissue to secure the wirelesselectrode assembly within a chamber of the heart; wherein the tissuefixation member comprises a flexible tine including a base, a tip and amedial portion extending therebetween; wherein the base of the tine issecured to the body between the first electrode and the secondelectrode; wherein the tine transitions from a straightened deliveryconfiguration to a curved deployed configuration; wherein the electricalstimulation system is configured to synchronize electrical stimulationto the heart provided with the wireless electrode assembly to electricalstimulation to the heart provided with the wired lead of the pulsegenerator.
 2. The system of claim 1, wherein the tip of the tine ispositioned distal of the base in the straightened deliveryconfiguration.
 3. The system of claim 1, wherein both the base of thetine and the first electrode remain immovably fixed to the body whilethe tine transitions from the straightened delivery configuration to thecurved deployed configuration.
 4. The system of claim 1, wherein thewireless electrode assembly further includes a circuit positioned withinthe body, and wherein the circuit is designed to deliver electricalenergy to the first electrode.
 5. A method of providing pacing therapyto a heart of a patient, comprising: implanting a wireless electrodeassembly into a chamber of the heart, the wireless electrode assemblyincluding: a body having a distal end region extending to a distal endof the body and a proximal end region extending to a proximal end of thebody; a first electrode secured to the distal end of the distal endregion of the body; a second electrode disposed on the proximal endregion of the body; and a tissue fixation member engaging cardiac tissueto secure the wireless electrode assembly within the chamber of theheart, the tissue fixation member comprising a tine including a base, atip and a medial portion extending therebetween; wherein the base issecured to the body between the first electrode and the secondelectrode; wherein the tine transitions from a straightened deliveryconfiguration while the wireless electrode assembly is being advanced tothe heart to a curved deployed configuration when the wireless electrodeassembly is implanted in the chamber of the heart; implanting a wiredlead extending from a pulse generator within the patient; providingelectrical stimulation to the heart with the wireless electrodeassembly; providing electrical stimulation to the heart with the wiredlead of the pulse generator; and synchronizing the electricalstimulation to the heart provided with the wireless electrode assemblyto the electrical stimulation to the heart provided with the wired leadof the pulse generator.
 6. The method of claim 5, wherein the pulsegenerator wirelessly communicates with a controller implanted in thepatient.
 7. The method of claim 6, wherein the controller communicateswith the wireless electrode assembly.
 8. The method of claim 7, whereinthe wireless electrode assembly includes a circuit designed to deliverelectrical energy provide electrical stimulation to the heart.
 9. Themethod of claim 5, further comprising: sensing an ECG signal with thepulse generator.
 10. The method of claim 5, wherein the wired lead isimplanted in a right atrium or right ventricle of the heart, and thewireless electrode assembly is implanted in a left atrium or leftventricle of the heart.
 11. The method of claim 5, further comprising:implanting a second wireless electrode assembly into another chamber ofthe heart.